Led light unit and method of replacing an led light unit

ABSTRACT

An LED light unit, in particular for a passenger transportation vehicle, such as an aircraft, a road vehicle, a ship or a rail car, has a support portion a light source having at least one LED, the light source being arranged on the support portion, and a refractive optical element having an inner surface and an outer surface the refractive optical element being attached to the support portion and being arranged over the light source. The refractive optical element has a chamfer portion adjacent the support portion, wherein at least one of the inner surface and the outer surface has at least one chamfer surface in the chamfer portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/250,837 filed Apr. 11, 2014, which claims priority to European PatentApplication No. 13166846.9 filed May 7, 2013, the entire contents ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to exterior lighting systems for passengertransport vehicles, such as aircraft, road vehicles, ships or rail cars.In particular, it relates to an LED light unit for such passengertransport vehicles.

BACKGROUND

Almost all passenger transport vehicles have exterior lights. They areprovided for a wide variety of different purposes, such as for allowingthe passengers and/or operators to view the outside, for passivevisibility, for signalling purposes, etc. In the aircraft industry andother fields, exterior lights are highly regulated in terms of the lightintensity distributions that are emitted from the lights.

LED light units have become common in the aircraft industry in recentyears. In order to satisfy the regulations, complex optical structureshave been developed that comprise various LED's, reflectors andshutters. These complex structures lead to LED light units that arecomplicated to manufacture and are fairly costly.

Accordingly, it would be beneficial to provide an LED light unit thathas improved means for conditioning the output light intensitydistribution. Further, it would be beneficial to provide a method ofreplacing existing LED light units, for example when they are used for along time or broken, with such improved LED light units, while keepingthe wiring of the power supply systems.

SUMMARY

Exemplary embodiments of the invention include an LED light unit, inparticular for a passenger transportation vehicle, such as an aircraft,a road vehicle, a ship or a rail car, comprising a support portion, alight source having at least one LED, the light source being arranged onthe support portion, and a refractive optical element having an innersurface and an outer surface, the refractive optical element beingattached to the support portion and being arranged over the lightsource. The refractive optical element has a chamfer portion adjacentthe support portion, wherein at least one of the inner surface and theouter surface has at least one chamfer surface in the chamfer portion.

A chamfer surface is generally a surface inclined with respect to theremainder of the refractive optical element. Providing such a chamfersurface, or a plurality of chamfer surfaces, allows for refracting thelight from the light source in the chamfer portion in a different manneras compared to the remainder of the refractive optical element. In thisway, the chamfer portion of the LED light unit alters the output lightintensity distribution in a manner different from the remainder of therefractive optical element. Providing at least one chamfer surface is aneffective means of conditioning the output light intensity distributionwithout shutters and reflectors inside of the refractive opticalelement. The at least one chamfer surface is inherently integrated withthe remainder of the refractive optical element, which refractiveoptical element can even be produced in one production step, e.g. byinjection molding. With the chamfer portion being positioned adjacentthe support portion, the improved way of conditioning the output lightintensity may in particular relate to an ambient light emissiondirection, which often is subject to particularly strict lightdistribution requirements. These requirements can be satisfied in animproved manner by the provision of the at least one chamfer surface.

The chamfer surface may have an inclination with respect to theremainder of the refractive optical element. As the refractive opticalelement may have a plurality of shapes, the inclined nature of thechamfer surface may also be defined in other ways. For example, achamfer surface may be a surface that is not orthogonal to the supportportion. In prior art embodiments, the inner surface and the outersurface of the refractive optical element form a substantially 90° anglewith the support portion at the border between the refractive opticalelement and the support portion. In other words, the inner surface andthe outer surface of prior art refractive optical elements areorthogonal to the support portion, where those elements meet. The termchamfer surface describes a structure that does not provide such anorthogonal relation with the support portion. The chamfer surface formsan angle other than 90° with the support portion.

The chamfer surface may also be referred to as inclined surface,bevelled surface or slanted surface.

Depending on the high-level structure of the refractive optical element,the chamfer surface may have different forms. For example, if therefractive optical element has an overall substantially rectangularcuboid shape, i.e. a box shape, the chamfer surface may be a planesurface. In another example, if the refractive optical element has anoverall substantially spherical shape, the chamfer surface may be anannular section of a cone. In both of these examples, the chamfersurface appears as a straight line in a cross section through therefractive optical element. Consequently, according to a particularembodiment, the chamfer surface may form a straight line in a crosssection through the refractive optical element, when the cross-sectionalplane is orthogonal to the support portion.

The chamfer surface may form a bend with respect to the remainder of therefractive optical element. This bend may be present in a cross-sectionthrough the refractive optical element. It may also extend along theentire chamfer surface. In mathematical terms, the bend may also becharacterized as a non-differentiable portion of the inner surface/outersurface. However, the bend may also be smooth, such that it is apparenton a large scale, although the inner surface/outer surface isdifferentiable in all points.

The expression that “at least one of the inner surface and the outersurface has at least one chamfer surface in the chamfer portion” mayinclude all of the following options. In particular, the inner surfacemay have exactly one chamfer surface. Alternatively or in addition, theouter surface may have exactly one chamfer surface. It is also possiblethat one or both of the inner surface and outer surface have a pluralityof chamfer surfaces. A plurality of chamfer surfaces may for example beprovided if the refractive optical element is not spherical, but cuboid.In that case, each side face may have its own chamfer surface(s), on theinside and/or the outside. It is also possible to have multiple chamfersurfaces on one or both of the inside and the outside of a generallyspherical refractive optical element. This may for example be the caseif different output light distributions are desired for different outputdirections.

The LED light unit may be suitable for the exterior of a passengertransport vehicle, such as an aircraft, a road vehicle, a ship or a railcar.

According to a further embodiment, the at least one chamfer surfaceextends around the entire perimeter of the refractive optical element.In particular, the inner surface of the refractive optical element mayhave one or more chamfer surface(s) that extend(s) around the entireperimeter of the refractive optical element. Alternatively/additionally,the outer surface of the refractive optical element may have one or morechamfer surface(s) that extend(s) around the entire perimeter. In thisway, the chamfer surface(s) may form an annular surface or a frame-likesurface or any other enclosed surface structure, comprised of one ormore chamfer surface(s). However, it is also possible that the chamfersurface(s) extend(s) around a portion of the perimeter, on the insideand/or on the outside. The combination is also possible. The at leastone chamfer surface may extend around the entire perimeter of the innersurface or the outer surface and extend around a portion of therespectively other one of the inner and outer surfaces.

According to a further embodiment, the chamfer portion extends at mostin the lower 50% of the refractive optical element, in particular atmost in the lower 40% of the refractive optical element. The terms lower50% and lower 40% refer to the portion of the height of the refractiveoptical element where the one or more chamfer surfaces are. In thiscontext, reference is made to the “height” of the refractive opticalelement and to the “lower” portion of the refractive optical elementunder the assumption that the refractive optical element is placed on aplane ground surface. The height is measured in the direction ofextension orthogonal to the support portion. Accordingly, the “lower”portion of the refractive optical element is the portion adjacent to thesupport portion. The expressions at most 50% and at most 40% mean 50% orless and 40% or less, respectively.

The extension of the chamfer portion may be defined in various ways.Besides measuring the extension as a portion of the height of therefractive optical element, it is also possible to provide an angularmeasure. The emitting direction of the light source orthogonal to thesupport portion is generally the emission direction with the highestlight intensity. This orthogonal direction is therefore also referred toas principal light emission direction. In a cross section through therefractive optical element, all points of the inner surface and of theouter surface can be defined by their angles with respect to theprincipal light emission direction. Accordingly, the extension of thechamfer portion may also be defined by its angular range with respect tothe principal light emission direction.

According to a particular embodiment, the chamfer portion extends in anangular range between 60° and 90° with respect to the principal lightemission direction. In a further particular embodiment, the chamferportion extends in an angular range between 70° and 90° with respect tothe principal light emission direction. The given angular ranges may bepresent in a plurality of cross sections through the refractive opticalelement or in all cross sections.

For some shapes of the refractive optical element, the differentextension definitions may be converted easily. For example, for agenerally spherical refractive optical element, the portion of theheight of the refractive optical element is the cosine of the lowerboundary value of the angular range. As a concrete example, a chamferportion extending in an angular range between 70° and 90° with respectto the principal light emission direction extends in the lower 34,2% ofthe refractive optical element.

The definition of the extension of the chamfer portion does not requirethat the defined portion of the refractive optical element is coveredentirely with one or more chamfer surfaces. It rather means that nochamfer surface(s) is/are present outside the chamfer portion.

According to a further embodiment, the refractive optical element has atleast one of the following four features. First, the inner surface ofthe refractive optical element may have an inwards slanted chamfersurface refracting the light of the light source towards the supportportion. Second, the inner surface of the refractive optical element mayhave an outwards slanted chamfer surface refracting the light of thelight source away from the support portion. Third, the outer surface ofthe refractive optical element may have an inwards slanted chamfersurface refracting the light of the light source towards the supportportion. Fourth, the outer surface of the refractive optical element mayhave an outwards slanted chamfer surface refracting the light of thelight source away from the support portion.

All of these four options of chamfer surfaces allow for an efficientreduction of the output light intensity of the LED light unit in anambient light emission direction. The term ambient light emissiondirection refers to a light emission direction far removed from theprincipal light emission direction. In other words, the ambient lightemission direction forms a large angle with the principal light emissiondirection. In particular embodiments, the ambient light emissiondirection may denote an angular range of more than 60° with theprincipal light emission direction, in particular of more than 70° withthe principal light emission direction.

The four options described allow for an efficient reduction of theoutput light intensity of the LED light unit in the ambient lightemission direction in the following ways. The inwards slanted chamfersurface on the inner surface of the refractive optical element refractsthe light, emitted from the light source, towards the support portion.It may be absorbed by the support portion or by the structure outsidethe LED light unit, to which the LED light unit is attached, dependingon the degree of inclination of the inwards slanted chamfer surface. Ineither case, this portion of the light from the light source does notcontribute to the output light intensity in the ambient light emissiondirection. Alternatively, the refracted light may be reflected by thesupport portion or by the structure outside the LED light unit. In thiscase, depending again on the inclination of the inwards slanted chamfersurface, the refracted light may be reflected in such a way that it doesnot or only partly contribute to the light emitted in the ambient lightemission direction.

The outwards slanted chamfer surface on the inner surface of therefractive optical element refracts the light away from the supportportion. In this way, it does not or to a lesser degree contribute tothe light emitted in the ambient light emission direction.

The inwards slanted chamfer surface on the outer surface of therefractive optical element refracts the light of the light sourcetowards the support portion. In this way, this light may hit the supportportion or the structure outside the LED light unit, to which the LEDlight unit is attached. The light may be absorbed there, in which caseit does not contribute to the light emitted in the ambient lightemission direction. Alternatively, the light may be reflected there, inwhich case it does not or to a lesser degree contribute to the lightemitted in the ambient light emission direction, depending on the angleat which the light hits the support portion or the structure outside theLED light unit.

The outwards slanted chamfer surface on the outer surface of therefractive optical element refracts the light of the light source awayfrom the support portion. In this way, it does not or to a lesser degreecontribute to the light emitted in the ambient light emission direction.

It is apparent that the amount of contribution to the light emitted inthe ambient light emission direction depends on the angular range viewedas the ambient light emission direction and the degree of inclination ofthe respective chamfer surface.

According to a particular embodiment, exactly one or an arbitrary subsetof the inwards slanted chamfer surface on the inner surface, of theoutwards slanted chamfer surface on the inner surface, of the inwardsslanted chamfer surface on the outer surface, and of the outwardsslanted chamfer surface on the outer surface may be present. All ofthese chamfer surfaces may be present partially or entirely around theperimeter of the inner surface and/or outer surface. In a particularembodiment, one inwards or outwards slanted chamfer surface may bepresent on each of the inner surface and the outer surface of therefractive optical element.

According to a further embodiment, the inwards slanted chamfer surfaceof the inner surface of the refractive optical element has such aninclination that it refracts the light from the light source to a bordersurface between the refractive optical element and the support portion.In this way, the absorption/reflection action of the refracted lighttakes place within the LED light unit. Accordingly, the LED light unithas a set output light intensity behavior, no matter if it is mounted onan absorptive or reflective structure for operation. It is also possiblethat the inwards slanted chamfer surface of the inner surface of therefractive element has such an inclination that the refracted light hitsthe support portion on the outside, but close to the refractive opticalelement. In this way, a support portion having a slightly largerextension than the lower portion of the refractive optical element leadsto an equally set output light intensity behavior, as discussed above.

According to a further embodiment, the support portion islight-absorbent, at least in a border surface between the refractiveoptical element and the support portion. The material of the supportportion may be light absorbent. Alternatively, the support portion mayhave a light-absorbent coating. The term light-absorbent may refer tothe property of absorbing a substantial amount of light irradiated ontothe support portion. In particular, it may denote an absorption of 90%or more of the irradiated light.

According to a further embodiment, the support portion is reflective, atleast in a border surface between the refractive optical element and thesupport portion. The material of the support portion may be reflective.Alternatively, the support portion may have a reflective coating.

According to a further embodiment, the light source has a source-sidelight intensity distribution, emitted from the light source inoperation, and the LED light unit has a desired light intensitydistribution, emitted from the LED light unit in operation, wherein theat least one chamfer surface is designed in such a way that a relativelight intensity of the desired light intensity distribution in anambient light emission direction is reduced as compared to a relativelight intensity of the source-side light intensity distribution in theambient light emission direction. The refractive optical element,comprising the at least one chamfer surface, carries out atransformation of the light intensity distribution of the light sourceinto an output light intensity distribution with differentcharacteristics. In particular, the refractive optical element may beshaped to transform the source-side light intensity distribution intothe desired light intensity distribution. By reducing the lightintensity in the ambient light emission direction, the LED light unit isable to satisfy light intensity distribution requirements that requirelower relative light intensities in the ambient light emission directionthan common light sources provide.

The term relative light intensity refers to the light intensity in agiven emission direction with respect to the light intensity in theprincipal light emission direction or with respect to the total lightintensity of the light source. Above described alteration of therelative light intensity distribution may be achieved with one or morechamfer surfaces on the inner surface or with one or more chamfersurfaces on the outer surface or with chamfer surfaces on the innersurface and the outer surface of the refractive optical element.

According to a further embodiment, the at least one chamfer surface isdesigned in such a way that substantially no light is emitted in theambient light emission direction. In this way, the LED light unit maysatisfy very restrictive regulations regarding the light emission in theambient light emission direction. Such restrictive regulations may forexample be encountered in the aviation regulations for commercial airplanes.

According to a further embodiment, the ambient light emission directionis an angular region of between 60° and 90°, in particular between 70°and 90°, with respect to a principal light emission direction of the LEDlight unit. As explained above, the principal light emission directionis generally the emission direction orthogonal to the support portionand running through the center of the light source.

According to a further embodiment, the desired light intensitydistribution is defined by at least two cross-sectional light intensitydistributions, the at least two cross-sectional light intensitydistributions comprising a first desired cross-sectional light intensitydistribution in a first cross-sectional plane and a second desiredcross-sectional light intensity distribution in a second cross-sectionalplane. The inner surface and the outer surface of the refractive opticalelement are shaped such that they jointly transform the source-sidelight intensity distribution into the desired light intensitydistribution. In a particular embodiment, at least one of the innersurface and the outer surface of the refractive optical element is notspherical. In this way, the conditioning of the output light intensitymay be extended from the chamfer portion of the refractive opticalelement to a larger portion of or even the entire refractive opticalelement. However, this does not mean that the at least one chamfersurface cannot provide for the transformation into the desired lightintensity distribution by itself. This depends on the desired lightintensity distribution in question. Having two specific cross-sectionaldesired light intensity distributions provides for efficient means of anextensive conditioning of the output light intensity distribution.

The desired light intensity distribution may be a light intensitydistribution that satisfies given light intensity requirements. In otherwords, a desired light intensity distribution fulfils or exceeds givenlight intensity requirements. With light intensity regulations oftenrequiring two light intensity distributions in particularcross-sectional planes, the definition of the desired light intensitydistribution by at least two cross-sectional light intensitydistributions allows for an effective adaptation of the LED light unitto the given requirements.

With the refractive optical element having a shape that provides for atransformation of the source-side light intensity distribution into thedesired light intensity distribution, the refractive optical elementensures that the emitted light complies with the given light intensityrequirements. In this way, the need for additional optical elementsbetween the light source and the refractive optical element may bedecreased or entirely eliminated. Moreover, the overall shaping of therefractive optical element for transforming the source-side lightintensity distribution into the desired light intensity distributionprovides a further degree of freedom for conditioning the output lightintensity distribution in addition to the provision of the at least onechamfer surface. In this way, the conditioning may extend beyond thechamfer portion.

Moreover, with the conditioning of the emitted light intensitydistribution via the refractive optical element, the emitted lightintensity distribution, i.e. the desired light intensity distribution inthe language of the present application, can be adapted to barelysatisfy the given requirements. In other words, the emitted lightintensity distribution may satisfy, but not or only just exceed thegiven requirements. This means that the light from the light source isrefracted in such a way that it exits the LED light unit right where itis needed for satisfying the given requirements. This in turn means thatthe light capacity of the LED/LED's in the LED light unit is efficientlyused. In this way, it is possible to use less powerful and thereforeless costly LED's. It is also possible to reduce the number of LED's, insome application scenarios to exactly one LED.

The orientation of the first and second cross-sectional planes may bedefined with respect to the support portion, which may be substantiallyplanar. In particular, the first and second cross-sectional planes maybe orthogonal to the substantially planar support portion. In thealternative, the orientation of the first and second cross-sectionalplanes may be defined with respect to the passenger transport vehicle orwith respect to the floor, on which the passenger transport vehiclestands. For example, the first cross-sectional plane may be a verticalplane, while the second cross-sectional plane may be parallel to thefloor, i.e. it may be a horizontal plane.

The term source-side light intensity distribution refers to the lightintensity distribution emitted by the light source in the absence offurther optical structures, in particular in the absence of therefractive optical element. The source-side light intensity distributionis present on the source side of the refractive optical element, i.e. onthe inside of the refractive optical element.

The term transforming of the light intensity distribution refers to analteration of the light intensity distribution merely through refractionat the inner and outer surfaces of the refractive optical element, withthe exception of reflection and/or absorption of light at the boundarysurface between the refractive optical element and the support portion.

In general, the first and second cross-sectional planes cut through thelight source. However, this is not necessary.

According to a further embodiment, the first desired cross-sectionallight intensity distribution and/or the second desired cross-sectionallight intensity distribution is an envelope curve enveloping a pluralityof required light intensity values. In other words, the first desiredcross-sectional light intensity distribution may be an envelope curve orthe second desired cross-sectional light intensity distribution may bean envelope curve or both may be envelope curves. The plurality ofrequired light intensity values may be represented by discrete pointvalues or by a step function or in any other suitable way. The pluralityof required light intensity values may be the same or different for thefirst and second cross-sectional planes.

By providing an envelope curve, a continuous desired light intensitydistribution is achieved. Such a continuous desired light intensitydistribution results in a continuous shape of the inner and outersurfaces of the refractive optical element. This in turn allows for aneasier and more accurate production as compared to non-continuoussurface shapes, in particular when the refractive optical element isinjection-molded.

Required light intensity values are generally defined in terms ofintensity values for particular angles. In this context, the angles aremeasured with respect to the principal light emission direction, asexplained above.

In more general terms, the first desired cross-sectional light intensitydistribution and/or the second desired cross-sectional light intensitydistribution may be continuous light intensity distributions.

According to a further embodiment, the first desired cross-sectionallight intensity distribution is at least as high as a first requiredlight intensity distribution, the first required light intensitydistribution defining minimum light intensity values for at least a partof the first cross-sectional plane. In this way, the first desiredcross-sectional light intensity distribution has higher or equal values,as compared to the first required light intensity distribution, acrossthe whole angular range in question, which may be a part or all of theangular range. Accordingly, if the first required light intensitydistribution specifies minimum values, it is ensured that those minimumvalues are respected across the whole applicable angular range.

However, it is also possible that the first required light intensitydistribution specifies allowable maximum light intensity values in thefirst cross-sectional plane or that the first required light intensitydistribution specifies a mix of minimum and maximum light intensityvalues or that the first required light intensity distribution specifiesan allowable corridor of light intensity values over the applicableangular range. In each of these cases, the first desired cross-sectionallight intensity distribution takes the given light intensityrequirements into account and satisfies these requirements. In this way,the alteration of the light intensity distribution via the refractiveoptical element leads to a desired light intensity distribution on itsoutside that conforms with the requirements.

According to a further embodiment, the second desired cross-sectionallight intensity distribution is at least as high as a second requiredlight intensity distribution, the second required light intensitydistribution defining minimum light intensity values for at least a partof the second cross-sectional plane. The second required light intensitydistribution defining minimum light intensity values may be present inaddition/as an alternative to the first required light intensitydistribution. All considerations given above with respect to the firstrequired light intensity distribution equally apply to the secondrequired light intensity distribution. Moreover, all given options forboth of these requirements may be combined freely. For example, one ofthe first and second required light intensity distributions may specifyminimum values, while the other of the two may specify maximum values.Any other combination is possible as well.

According to a further embodiment, the inner surface of the refractiveoptical element has a circular shape in the first cross-sectional plane,with the outer surface of the refractive optical element being shaped inthe first cross-sectional plane such that the inner surface and theouter surface transform the source-side light intensity distribution inthe first cross-sectional plane into the first desired cross-sectionallight intensity distribution. For a light source that emits lightradially outwards, a spherical surface does not change the lightintensity distribution, as all light rays hit the spherical surface atan angle of 90°. Accordingly, the outer surface alone performs thetransformation of the source-side light intensity distribution into thefirst desired cross-sectional light intensity distribution. Thisconcentration of the transformation on the outer surface makes thedetermination of the shape of the outer surface in the firstcross-sectional plane easier than in the case where both surfacescontribute to the transformation. Accordingly, this allows for a lesscomplex design and production process.

According to a further embodiment, the outer surface of the refractiveoptical element has a circular shape in the second cross-sectionalplane, with the inner surface of the refractive optical element beingshaped in the second cross-sectional plane such that the inner surfaceand the outer surface transform the source-side light intensitydistribution in the second cross-sectional plane into the second desiredcross-sectional light intensity distribution. Both surfaces contributeto the transformation of the source-side light intensity distributioninto the second desired cross-sectional light intensity distribution.With the outer surface having a circular cross-section, it iswell-behaved and easy to handle. While contributing to thetransformation, it still allows for a manageable design and productionprocess of the inner surface and the refractive optical element as awhole.

According to a further embodiment, both the inner surface and the outersurface of the refractive optical element are not spherical. This doesnot exclude that both of these surfaces may have circular shapes inparticular cross-sections. In a particular embodiment, the inner surfacehas a circular shape in the first cross-sectional plane and anon-circular shape in the second cross-sectional plane, while the outersurface has a circular shape in the second cross-sectional plane and anon-circular shape in the first cross-sectional plane. As describedabove, the combination of the respective circular and non-circularsurfaces perform the desired transformation of the light intensitydistribution in the respective cross-sectional planes. By combiningcircular and non-circular cross-sections in the described manner, arefractive optical element with low thickness variation may be provided.Such low thickness variation allows for an accurate and comparably easyproduction of the refractive optical element, especially when it isinjection-molded.

According to a further embodiment, the thickest portion of therefractive optical element is less than 3 times as thick as the thinnestportion of the refractive optical element. Such a maximum thicknessvariation of 3 allows in particular for an accurate and comparably easyproduction of the refractive optical element, especially when it isinjection-molded.

It is pointed out that it is also possible that one of the inner surfaceand the outer surface is entirely spherical, with the other of the innerand outer surfaces having a shape that ensures the transformation of thesource-side light intensity distribution into the desired lightintensity distribution. In this case, said other of the inner and outersurfaces comprises the at least one chamfer surface.

According to a further embodiment, the first cross-sectional plane isperpendicular to the second cross-sectional plane. In this way, thelight intensity value requirements affect a large portion of the lightemitting region of the LED light unit. A widespread conditioning of thelight intensity, emitted from the LED light unit, is achieved with theprovision of only two cross-sectional light intensity distributions.

According to a further embodiment, the first cross-sectional plane is avertical cross-sectional plane and the second cross-sectional plane is ahorizontal cross-sectional plane. In particular, the definitions ofvertical and horizontal may apply to the orientation of the first andsecond cross-sectional planes with respect to the floor on which thepassenger transport vehicle stands. In other words, the terms horizontaland vertical may have the underlying assumption that the LED light unitis placed on a substantially vertical wall portion of the passengertransport vehicle. Accordingly, the vertical and horizontalcross-sectional planes may not be vertical and horizontal, when the LEDlight unit is provided by itself. In particular, this use of the termshorizontal and vertical is different from the use of the terms heightand lower portion, as used above for describing the position of thechamfer portion.

According to a further embodiment, the inner surface and the outersurface of the refractive optical element are continuous surfaces. Inparticular, the inner surface and the outer surface may be surfacesenveloping the cross sections of the inner and outer surface of therefractive optical element in the first and second cross-sectionalplanes. In other words, the contours of the refractive optical elementin the first and second cross-sectional planes, resulting from thedesired cross-sectional light intensity distributions in these planes,are part of the continuous inner and outer surfaces of the refractiveoptical elements. In particular, the inner and outer surfaces of therefractive optical element may be continuous and differentiable betweenthe first and second cross-sectional planes. They may be smooth andwithout sharp contours. In this way, the inner surface and the outersurface may be suitably produced by various manufacturing methods, inparticular by injection-molding.

It is also possible that the inner surface and the outer surface of therefractive optical element are not shaped over much or all of theirextension such that they jointly transform the source-side lightintensity distribution into the desired light intensity distribution, asdescribed in various embodiments in the preceding paragraphs. Inparticular, it is possible that the refractive optical element has aconstant thickness with the exception of the chamfer portion. Thechamfer surfaces are by definition inclined with respect to theremainder of the refractive optical element and therefore generally leadto a thickness variation in the chamfer portion.

The refractive optical element may have a wide variety of shapes.According to a particular embodiment, the refractive optical element isgenerally spherical. According to another particular embodiment, therefractive optical element is generally cuboid or box-shaped. It is ingeneral a convex structure having a hollow space to the inside, i.e.towards the light source. The terminology “generally spherical” and“generally cuboid or box-shaped” reflects the fact that the refractiveoptical element is not entirely spherical or entirely box-shaped due tothe presence of the at least one chamfer surface. The terminology“generally spherical” and “generally cuboid or box-shaped” refers to thehigh level impression of the refractive optical element at first glance.

According to a further embodiment, the refractive optical elementextends over a solid angle of 2π. In other words, the refractive opticalelement extends over half of the total solid angle of 4π, the totalsolid angle of 4π denoting the entirety of all directions in 3dimensions. In yet other words, the refractive optical element fullyencloses the light source, when placed on a plane support portion. It ishowever pointed out that the refractive optical element may also extendover a solid angle of less or more than 2π.

According to a further embodiment, the diameter of the refractiveoptical element at the support portion is between 10 and 30 mm, inparticular between 10 and 20 mm. The diameter denotes the largestextension of the refractive optical element at the support portion,irrespective of the shape of the refractive optical element. The shapeand size of the refractive optical element may depend on the number andpositioning of the one or more LED's of the light source. In general,the described embodiments allow for the provision of an extremelycompact LED light unit for given light intensity requirements.

It is pointed out that different materials with different refractiveindices may be used for the refractive optical element. It is apparentthat the refractive index plays an important role in defining the shapeof the refractive optical element and the inclination angles of the atleast one chamfer surface. Exemplary materials of the refractive opticalelements are Polycarbonate and Poly(methyl methacrylate), also referredto as PMMA. The refractive indices of these materials are around 1.5, inparticular between 1.45 and 1.6.

According to a further embodiment, the light source is one single LED.In particular, the one single LED may be arranged in the center of therefractive optical element. A single LED has a light intensitydistribution that is well-behaved and can be handled in a particularlygood way. Therefore, a single LED leads to less complex of a geometryfor the refractive optical element in general and for the at least onechamfer surface in particular. It is pointed out that it is alsopossible that the light source comprises a plurality of LED's, inparticular in a chain arrangement.

In general, it is pointed out that the total light intensity of thelight source has to be sufficient for satisfying the total requiredlight intensity. The refractive optical element cannot increase thetotal light intensity. It is not an active element. It can only redirectthe emitted light in a particularly advantageous way such that the totallight intensity of the light source is used with great efficiency forthe purpose of satisfying the light intensity requirements.Consequently, the number and kind of LED's used for the light sourcedepends partly on the given requirements.

According to a further embodiment, a space between the light source andthe refractive optical element is free of shutters and reflectors. Thisallows for an efficient use of the total light intensity of the lightsource and for the minimization of optical components. The LED lightunit may be more energy-efficient and less costly to produce.

According to a further embodiment, the power consumption of the LEDlight unit is between 1W and 10W, in particular between 2W and 5W, andmore in particular around 3W.

Exemplary embodiments of the inventions further include a passengertransport vehicle, such as an aircraft, a road vehicle, a ship or a railcar, having at least one LED light unit, as described in any of theembodiments above, the at least one LED light unit being an exteriorlight of the passenger transport vehicle, i.e. being positioned in theexterior of the passenger transport vehicle. The LED light unit may beattached to the outer surface or outer wall or shell structure of thepassenger transport vehicle. The aircraft may be an air plane or ahelicopter. The road vehicle may be a bus, a truck or a car. The LEDlight unit may in particular be a rear navigation light unit of an airplane. Above modifications and advantages equally relate to thepassenger transport vehicle.

Exemplary embodiments of the invention further include a method ofreplacing a used light unit, in particular in a passenger transportvehicle, such as an aircraft, a road vehicle, a ship or a rail car, withan LED light unit, as described in any of the embodiments above, themethod comprising the steps of disconnecting the used light unit from apower source, and connecting the LED light unit, as described in any ofthe embodiments above, to the power source. In this way, new improvedLED light units can be included into existing passenger transportvehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in greater detail below withreference to the figures, wherein:

FIGS. 1a to 1d show cross-sectional views through exemplary LED lightunits in accordance with the invention.

FIG. 2 shows a perspective view of an exemplary refractive opticalelement in accordance with the invention.

FIGS. 3a and 3b show two cross-sectional views through an exemplary LEDlight unit in accordance with the invention.

FIG. 4 shows a light intensity distribution of an LED, as used in anexemplary LED light unit in accordance with the invention.

FIGS. 5a and 5b show the respective required light intensitydistributions and the respective desired light intensity distributionsin two cross-sectional planes in accordance with an exemplary refractiveoptical element in accordance with the invention.

DETAILED DESCRIPTION

All of the FIGS. 1a to 1d show exemplary LED light units, generallydesignated by reference numeral 2. The LED light unit 2 comprises asupport portion 4, a light source 6, and a refractive optical element 8.In the exemplary embodiments of FIG. 1, the light source 6 is a singleLED. However, it is also possible to provide a plurality of LED's as thelight source 6, in particular in a chain arrangement.

The refractive optical element 8 has a generally spherical shape. It hasan inner surface 82 and an outer surface 84, which form substantially ahalf of a hollow sphere.

The refractive optical element 8 further has a chamfer portion 90, whichcomprises a chamfer surface 92. The chamfer surface 92 is an inwardsslanted chamfer surface on the inner surface 82 of the refractiveoptical element 8. The chamfer surface 92 is referred to as an inwardsslanted chamfer surface, because it is disposed further inwards than theinner surface 82 would be if the refractive optical element 8 were aperfectly shaped hollow sphere half. In this context, it is pointed outthat the refractive optical element 8 is referred to as “generallyspherical”, because it has the shape of a partial hollow sphere with theexception of the chamfer portion 90, in particular with the exception ofthe provision of the chamfer surface 92.

In the viewing direction of FIG. 1, the refractive optical element 8 isshown to be placed on top of the support portion 4. Accordingly,reference will be made in the following to a lower portion and an upperportion of the refractive optical element 8. However, it is pointed outthat this nomenclature does not require the support portion to be belowthe refractive optical element 8 in operation. For example, the LEDlight unit 2 may be attached to a vertical mounting structure, such asan outside wall of an air plane or the like. In that case, therefractive optical element 8 comes to lie laterally from the supportportion 4.

FIG. 1 further shows a principal light emission direction 60 and aborderline 62 between an ambient light emission direction and anon-ambient light emission direction. The ambient light emissiondirection is below the borderline 62 in the orientation of FIG. 1.

The principal light emission direction 60 is orthogonal to the supportportion 4 and extends through the center of the LED 6. It is referred toas principal light emission direction, because conventional LED's havetheir highest light intensity in a direction of emission orthogonal totheir positioning on a support structure. However, it is pointed outthat the term principal light emission direction herein generally refersto a direction orthogonal to the support portion 4 and extending throughthe light source 6, in particular through the center of the lightsource.

The direction of the borderline 62 encloses an angle of 70° with theprincipal light emission direction 60, seen from the center of the LED6. Accordingly, the ambient light emission direction encompasses allemission directions that have an angle of 70° and more with respect tothe principal light emission direction 60. Due to the support portion 4being a plane to which the LED 6 is attached, the ambient light emissiondirection encompasses all directions that have an angle of between 70°and 90° with the principal light emission direction 60.

It can be seen that the chamfer surface 92 is provided in a portion ofthe refractive optical element 8 that also has an angle of more than 70°with respect to the principal light emission direction 60. The chamferportion 90, which is the portion of the refractive optical element 8that comprises the chamfer surface 92, also extends in a portion of therefractive optical element 8 that has an angle of more than 70° withrespect to the principal light emission direction 60. In terms of theheight of the refractive optical element 8, the chamfer portion extendswithin ca. 32% of the height of the refractive optical element, inparticular in the lower portion thereof. The lower portion is alsoreferred to as the portion adjacent to the support portion 4. It isapparent that the term height refers to the orientation of the LED lightunit 2 as given in FIG. 1. If the LED light unit 2 is orienteddifferently, such as for example during use on the exterior of apassenger transport vehicle, the “height” in the sense of thisapplication may not be a vertical direction.

The chamfer surface 92 is shown as two lines in the cross section ofFIG. 1a , one to the right and one to the left of the LED 6. These twolines indicate a chamfer surface that extends around the entireperimeter of the generally spherical refractive optical element 8. Inthis way, the chamfer surface 92 is in the form of a section of a cone.Since the upper end of the chamfer surface 92 is further removed fromthe principal light emission direction 60 than the lower end of thechamfer surface 92, the chamfer surface 92 is referred to as an inwardslanted chamfer surface.

The effect of the chamfer surface 92 in operation will be described asfollows. In particular, reference is made to an exemplary light ray 52,whose path from the LED 6 to the refractive optical element andtherethrough is shown. It is pointed out that the path of the light ray52 is not too scale and the refraction somewhat exaggerated forillustration purposes. The light ray 52 extends from the LED 6 to thechamfer surface 92 in a straight line. At the chamfer surface 92, it isrefracted towards the support portion 4, which it hits at a bordersurface between the support portion 4 and the refractive optical element8. The light ray 52 is reflected at this border surface between thesupport portion 4 and the refractive optical element 8, from where ittravels to the outer surface 84 of the refractive optical element 8,where it is slightly refracted again.

As can be seen, the output direction of the light ray 52 is more towardsthe principal light emission direction than the initial portion of thelight ray 52, as emitted from the LED 6. In other words, the outputdirection of the light ray 52 encloses a smaller angle with theprincipal light emission direction 60 than the original emissiondirection from the LED 6. In particular, the outside emission directionof the light ray 52 has an angle with the principal light emissiondirection 60 that is reduced in so much as compared to the originalemission direction that this light ray does not contribute to theambient light emission. This can also be seen from the fact that thelight ray 52 will cross the borderline 62 to the outside of therefracted optical element 8. In this way, light rays that initially fallinto the ambient light emission direction are redirected in such a waythat they ultimately end up outside of the ambient light emissiondirection.

It is also possible that the support portion 4 is light absorbent. Inthat case, the light ray 52 hits the absorbent surface of the supportportion 4 at the border surface between the refractive optical element 8and the support portion 4. The light ray 52 would end at this bordersurface and would also not contribute to light emitted in the ambientlight emission direction.

The LED light unit 2 of FIG. 1b is an alteration as compared to the LEDlight unit 2 of FIG. 1a . Like elements are denoted with like referencenumerals. In particular, the support portion 4 and the LED 6 are thesame in FIG. 1b as compared to FIG. 1a . Also, the refractive opticalelement 8 of FIG. 1b is the same as compared to the refractive opticalelement of FIG. 1a , with the exception of the chamfer portion 90.Therein, the inwards slanted chamfer surface 92 of FIG. 1a is replacedwith an outwards slanted chamfer surface 94. The outwards slantedchamfer surface 94 is also provided on the inner surface 82 of therefractive optical element 8.

The chamfer surface 94 is referred to as outwards slanted, because theupper end of the chamfer surface 94 is closer to the principal lightemission direction 60 than the lower end of the chamfer surface 94. Itis also referred to as outwards slanted, because it is further removedfrom the principal light emission direction than a perfectly sphericalinner surface of the refractive optical element would be in that part.Again, the chamfer surface 94 is depicted with two straight lines in thecross sectional view of FIG. 1b . With the refractive optical element 8having a generally spherical structure, the chamfer surface 94 extendsaround the entire perimeter of the inner surface 82 of the refractiveoptical element 8, having the shape of a section of a cone.

The effect of the chamfer surface 94 in operation is described asfollows. An exemplary light ray 54 is depicted, whose path is not tooscale and whose refraction is somewhat exaggerated for illustrativepurposes. The light ray 54 extends from the LED 6 to the chamfer surface94 in a straight line. It is refracted at the chamfer surface 94 in sucha way that its path is bent away from the support portion 4. The lightray 54 then travels to the outer surface 84 where it is again slightlyrefracted. The overall refraction of the light ray 54 has the effectthat the output emission direction is not within the ambient lightemission direction. In other words, the emission direction of the lightray 54 is altered in such a way as compared to the initial emissiondirection that the angle between the emission direction and theprincipal light emission direction 60 is decreased. Consequently, thelight ray 54 does not contribute to the light emitted in the ambientlight emission direction.

The LED light unit 2 of FIG. 1c is an alteration as compared to the LEDlight unit 2 of FIG. 1a . Like elements are denoted with like referencenumerals. In particular, the support portion 4 and the LED 6 are thesame in FIG. 1c as compared to FIG. 1a . Also, the refractive opticalelement 8 of FIG. 1c is the same as compared to the refractive opticalelement of FIG. 1a , with the exception of the chamfer portion 90.Therein, the inwards slanted chamfer surface 92 on the inner surface 82of FIG. 1a is replaced with an inwards slanted chamfer surface 96 on theouter surface 84 of the refractive optical element 8.

The chamfer surface 96 is referred to as inwards slanted for the samereasons as the chamfer surface 92, discussed above. Again, the chamfersurface 96 is depicted with two straight lines in the cross sectionalview of FIG. 1c . With the refractive optical element 8 having agenerally spherical structure, the chamfer surface 96 extends around theentire perimeter of the outer surface 84 of the refractive opticalelement 8, having the shape of a section of a cone.

The effect of the chamfer surface 96 in operation is described asfollows. An exemplary light ray 56 is depicted, whose path is not tooscale and whose refraction is somewhat exaggerated for illustrativepurposes. The light ray 56 extends from the LED 6 to the inner surface82 in a straight line. It is not refracted at the inner surface 82,because it hits the inner surface 82 at a right angle. Accordingly, thelight ray 56 keeps travelling straight to the outer surface 84 where ithits the chamfer surface 96. The chamfer surface 96 has such aninclination that the light ray 56 is refracted towards the supportportion 4 and hits the support portion 4 shortly after leaving therefractive optical element 8. The support portion 4 is absorbent, suchthat the light ray 56 ends at the support portion 4. Overall, therefraction of the light ray 56 has the effect that the light is absorbedby the support portion. Consequently, the light ray 56 does notcontribute to the light emitted in the ambient light emission direction.

The LED light unit 2 of FIG. 1d is an alteration as compared to the LEDlight unit 2 of FIG. 1a . Like elements are denoted with like referencenumerals. In particular, the support portion 4 and the LED 6 are thesame in FIG. 1d as compared to FIG. 1a . Also, the refractive opticalelement 8 of FIG. 1d is the same as compared to the refractive opticalelement of FIG. 1a , with the exception of the chamfer portion 90.Therein, the inwards slanted chamfer surface 92 on the inner surface 82of FIG. 1a is replaced with an outwards slanted chamfer surface 98 onthe outer surface 84 of the refractive optical element 8.

The chamfer surface 98 is referred to as outwards slanted for the samereasons as the chamfer surface 94, discussed above. Again, the chamfersurface 98 is depicted with two straight lines in the cross sectionalview of FIG. 1d . With the refractive optical element 8 having agenerally spherical structure, the chamfer surface 98 extends around theentire perimeter of the outer surface 84 of the refractive opticalelement 8, having the shape of a section of a cone.

The effect of the chamfer surface 98 in operation is described asfollows. An exemplary light ray 58 is depicted, whose path is not tooscale and whose refraction is somewhat exaggerated for illustrativepurposes. The light ray 58 extends from the LED 6 to the inner surface82 in a straight line. It is not refracted at the inner surface 82,because it hits the inner surface 82 at a right angle. Accordingly, thelight ray 58 keeps travelling straight to the outer surface 84 where ithits the chamfer surface 98. It is refracted at the chamfer surface 98in such a way that its path is bent away from the support portion 4. Therefraction of the light ray 58 has the effect that the output emissiondirection is not within the ambient light emission direction. In otherwords, the emission direction of the light ray 58 is altered in such away as compared to the initial emission direction that the angle betweenthe emission direction and the principal light emission direction 60 isdecreased. Consequently, the light ray 58 does not contribute to thelight emitted in the ambient light emission direction (assuming asubstantial distance from the LED light unit 2).

Accordingly, all four exemplary embodiments of FIGS. 1a to 1d showchamfer surfaces that keep at least a portion of the light away from theambient light emission direction that would be present if the refractiveoptical element were perfectly spherical. In other words, the chamfersurfaces decrease the relative light intensity in the ambient lightemission direction as compared to the relative light intensity of thelight source in this direction. The inclination angles for the chamfersurfaces 92, 94, 96 and 98 depend on various factors, such as therefractive index of the material of the refractive optical element andthe particular nature of the desired output light intensitydistribution.

While the four embodiments of FIG. 1 each show exactly one chamfersurface, either disposed on the inner surface or on the outer surface,it is also possible to combine different chamfer surfaces. For example,an inwards slanted chamfer surface on the inner surface and an inwardsslanted chamfer surface on the outer surface may jointly lead to arefraction where much light is absorbed by the support portion and doesnot contribute to the output in the ambient light emission direction. Inanother example, an outwards slanted chamfer surface on the innersurface and outwards slanted chamfer surface on the outer surface mayjointly redirect much light into the non-ambient light emissiondirection. In yet another example, an inwards slanted chamfer surface onthe inner surface may lead to absorption of light at the border surfacebetween refractive optical element and support portion, as discussedabove. An additional outwards slanted chamfer surface on the outersurface may then redirect light that is just not absorbed by the supportportion into the non-ambient light emission direction.

It is further pointed out that the chamfer surfaces do not have toextend around the entire perimeter of the refractive optical element. Inthe case of a generally spherical refractive optical element, thechamfer surface does not have to have the shape of a section of a cone.In particular, it is possible that the chamfer surface extends around aportion of the perimeter only. In this case, the chamfer surfaceconditions the output light intensity distribution only in a portion ofall cross sections through the LED light unit. An example for such acase will be discussed below.

FIG. 2 shows a perspective view of an another exemplary refractiveoptical element 8 in accordance with the invention. The refractiveoptical element 8 is shown without a light source and without a supportportion. Accordingly, only a part of the LED light unit 2 is shown inFIG. 2.

The refractive optical element has an inner surface 82 and an outersurface 84. The inner surface 82 and the outer surface 84 are bothnon-spherical. This can be seen from the surfaces themselves and alsofrom the contours on the support-side end of the inner and outersurfaces 82 and 84 (shown on top in the viewing direction of FIG. 2).These end contours of the inner surface 82 and the outer surface 84 arenot circular, but elliptical. This shows that both the inner surface 82and the outer surface 84 are not spherical. By not being spherical, theentirety of the inner surface 82 and the outer surface 84 play a role inconditioning the output light intensity, not only the chamfer surface.This will be explained in more detail below with respect to FIGS. 3-5.

A first cross-sectional plane 86 and a second cross-sectional plane 88are indicated by lines. The geometry of the inner and outer surfaces 82and 84 along the first and second cross-sectional planes 86 and 88 willbe described in detail with respect to FIG. 3.

FIG. 3 shows an exemplary LED light unit 2 in accordance with theinvention in two different cross-sections. The LED light unit 2 has asupport portion 4, a light source 6, and the refractive optical element8. The support portion 4 has a planar surface, to which the light source6 and the refractive optical element 8 are attached.

The light source 6 is a single LED. The refractive optical element 8,which has the inner surface 82 and the outer surface 84, is arrangedover the LED 6. Keeping the perspective view of FIG. 2 in mind, it isapparent that the refractive optical element 8 forms a completeenclosure around the LED 6 on the support portion 4.

FIG. 3a shows a cross-section through the LED light unit 2 along thefirst cross-sectional plane 86, referenced in FIG. 2. This cross-sectionis also referred to as vertical cross-section, because thecross-sectional plane 86 is intended to be a vertical plane, when theLED light unit 2 is in use, i.e. when the LED light unit 2 is mounted tothe exterior of a passenger transport vehicle.

The inner surface 82 of the refractive optical element 8 is circular inthe vertical cross-section of FIG. 3a . With the single LED 6 emittinglight radially, no refraction takes place at the inner surface 82 inthis cross-section. The outer surface 84 is non-circular in the verticalcross-section and performs a transformation of the light intensitydistribution of the LED 6, i.e. the source-side light intensitydistribution, into the first desired cross-sectional light intensitydistribution, which will be explained in detail below.

The refractive optical element 8 has a varying thickness in the verticalcross-section. The radius of the circular contour of the inner surface82 is denoted r. The radius r is between 5 and 6 mm in the exemplaryembodiment of FIG. 3. The thickness of the refractive optical elementright above the LED 6 (“above” referring to the orientation in thedrawing of FIG. 3), i.e. the thickness of the portion of the refractiveoptical element 8 farthest removed from the support portion 4, isdenoted with t1, which is 0,38*r in the exemplary embodiment of FIG. 3.In contrast thereto, the refractive optical element 8 has a thickness t2right at the support portion 4, which thickness t2 is 0,63*r in theexemplary embodiment of FIG. 3. The contour of the outer surface 84 andthe related variation in thickness of the refractive optical element 8provide for the desired transformation of the light intensitydistribution in the first cross-sectional plane, which will be describedin more detail below.

FIG. 3b is another cross-section through the LED light unit 2 along thesecond cross-sectional plane 88, shown in FIG. 2. This secondcross-sectional plane is also referred to as horizontal cross-sectionalplane, because this plane is intended to come to lie horizontally whenthe LED light unit is in use, i.e. when the LED light unit is attachedto the passenger support vehicle.

The outer surface 84 is circular in the horizontal cross-section of FIG.3b . The inner surface 82 is non-circular, such that the light emittedradially from the LED 6 is refracted at the inner surface 82. Therefracted light is then again refracted at the outer surface 84. In thisway, the inner surface 82 and the outer surface 84 jointly transform thesource-side light intensity distribution of the LED 6 into the seconddesired cross-sectional light intensity distribution, which will bedescribed in greater detail below.

The refractive optical element 8 has a chamfer portion 90. Inparticular, an outwards slanted chamfer surface 94 is disposed on theinner surface 82 of the refractive optical element 8. This chamfersurface 94 has the effects described above with respect to the chamfersurface 94 of FIG. 1 b.

As already described with respect to FIG. 3a , the thickness tl of therefractive optical element at the portion farthest removed from thesupport portion 4 is 0.38*r. In the horizontal cross-section, thethickness of the refractive optical element 8 right at the supportportion 4, which is denoted t3, is 0.25*r.

When comparing t2 and t3, it can be seen that the thickest portion ofthe refractive optical element 8 is less than three times as thick asthe thinnest portion of the refractive optical element 8. Such a lowvariation in thickness allows for a comparably easy production of therefractive optical element 8, in particular through injection moulding.

As can be seen from FIG. 2, the refractive optical element 8 has acontinuous and differentiable inner and outer surface 82 and 84 betweenthe first and second cross-sectional planes 86 and 88.

The transformation of the source-side light intensity distribution, i.e.of the emitted light intensity distribution of the LED 6, into thedesired light intensity distribution is explained with respect to FIGS.4 and 5.

FIG. 4 shows the source-side light intensity distribution LISS of theLED 6. This source-side light intensity distribution LISS is the lightintensity distribution as emitted by the LED 6. In the exemplaryembodiment, it is a typical Lambertian intensity distribution. FIG. 4represents a radial section cut where the light intensity is shown as afunction of an angular value. This angular value is an emittingdirection, measured with respect to the principal light emissiondirection, as explained above. The angle with respect to the principallight emission direction is the angle given on the x-axis of FIG. 4.

As can be seen from FIG. 4, the light intensity of the LED 6 is thegreatest in the direction perpendicular to the support portion 4, i.e.in the principal light emission direction. It decreases in emittingdirections deviating from that perpendicular direction. The source-sidelight intensity distribution of FIG. 4 is equally valid for the firstcross-sectional plane of FIG. 3a and for the second cross-sectionalplane of FIG. 3 b.

FIGS. 5a and 5b show the light intensity requirements for the verticaland horizontal directions as given by Federal Aviation Regulation (FAR)25.1385. It is explicitly pointed out that this regulation is an exampleonly. Moreover, these light intensity requirements may not only arisefrom regulations, but may also arise from other product designconsiderations in general.

FIG. 5a shows the vertical required light intensity distributionLIreq,ver, as required by above-mentioned Federal Aviation Regulation.The vertical required light intensity distribution LIreq,ver, which isin a more general term referred to as first required light intensitydistribution in the present application, is a step function givingrequired light intensity values for particular angular ranges. Theangular scale on the x-axis corresponds to the angular scale of FIG. 4,explained above.

The required vertical light intensity distribution is a set of minimumlight intensity values that the LED light unit has to emit in useaccording to the FAR.

FIG. 5a further shows a desired vertical light intensity distributionLIdes,ver which is in a more general term referred to as first desiredcross-sectional light intensity distribution throughout thisapplication. The desired vertical light intensity distribution LIdes,verenvelopes the required vertical light intensity distribution. Theenvelope curve is above the required vertical light intensitydistribution LIReq,ver across the entire angular range. In this way, acontinuous light intensity distribution is provided that satisfies alllight intensity requirements, but only exceeds those requirements to avery low degree. Therefore, this desired vertical light intensitydistribution LIdes,ver satisfies the light intensity requirements withvery good efficiency.

Reference is made again to FIG. 3a in connection with FIG. 4 and FIG. 5a. The shape of the outer surface 84 in the vertical cross-section ofFIG. 3a has a shape that transforms the source side light intensitydistribution LISS of FIG. 4 into the desired vertical light intensitydistribution LIdes,ver of FIG. 5a . In other words, the shape of theouter surface 84 is defined as the particular shape that achieves atransformation between exactly those two light intensity distributions.

Analogous considerations apply to the second set of light intensityrequirements, given in FIG. 5b . FIG. 5b shows the horizontal requiredlight intensity distribution LIreq,hor, as required by above-mentionedFederal Aviation Regulation. The horizontal required light intensitydistribution LIreq,hor, which is in a more general term referred to assecond required light intensity distribution in the present application,is a step function giving required light intensity values for particularangular ranges. Again, the angular scale on the x-axis corresponds tothe angular scale of FIG. 4, explained above.

The required horizontal light intensity distribution is a set of minimumlight intensity values that the LED light unit has to emit in useaccording to the FAR.

FIG. 5b further shows a desired horizontal light intensity distributionLIdes,hor which is in a more general term referred to as second desiredcross-sectional light intensity distribution throughout thisapplication. The desired horizontal light intensity distributionLIdes,hor envelopes the required horizontal light intensitydistribution. The envelope curve is above the required horizontal lightintensity distribution LIreq,hor. In this way, a continuous lightintensity distribution is provided that satisfies all light intensityrequirements, but only exceeds those requirements to a very low degree.Therefore, this desired horizontal light intensity distributionLIdes,hor satisfies the light intensity requirements with very goodefficiency.

Reference is made again to FIG. 3b in connection with FIG. 4 and FIG. 5b. The shape of the inner surface 82 in the horizontal cross-section ofFIG. 2b has a shape that transforms the source side light intensitydistribution LISS of FIG. 4 together with the circular outer surface 84into the desired horizontal light intensity distribution LIdes,hor ofFIG. 5b . In other words, the shape of the inner surface 82 is definedas the particular shape that achieves a transformation between exactlythose two light intensity distributions in cooperation with the circularouter surface 84.

Particular reference is made to FIG. 5b in combination with FIG. 3b forthe effect of the chamfer surface 94. As can be seen from FIG. 5b , thedesired horizontal light intensity distribution LIdes,hor is zero forangular values greater than ca. 70°. This is in line with a furtherrequirement of the FAR that the ambient light in the horizontal lightemission plane, i.e. the light in emission directions with an angle ofmore than 70° with respect to the principal light emission direction inthe horizontal plane, has to be zero. It is pointed out that thisrequirement does not exist for all exterior lights, but for some. Thechamfer surface 94 is an outwards slanted chamfer surface and thusrefracts light away from the support portion 4. In this way, the chamfersurface 94 helps in keeping the light emission direction with angularvalues of more than 70° in the horizontal plane free from emitted light.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. An LED light unit, comprising: a support portion, a light sourcehaving at least one LED, the light source being arranged on the supportportion, and a refractive optical element having an inner surface and anouter surface, the refractive optical element being attached to thesupport portion and being arranged over the light source, wherein therefractive optical element has a chamfer portion adjacent the supportportion, wherein at least one of the inner surface and the outer surfacehas at least one chamfer surface in the chamfer portion in a firstcross-sectional plane, wherein the LED light unit is an airplane rearnavigation light unit having an airplane rear navigation light intensitydistribution as defined by Federal Aviation Regulations 25.1391 and25.1393, as in force on May 7, 2013, and wherein the at least onechamfer surface refracts light away from an ambient light emissiondirection of the airplane rear navigation light intensity distributionin the first cross-sectional plane, wherein the ambient light emissiondirection is an angular region of between 70° and 90° with respect to aprincipal light emission direction of the airplane rear navigation lightintensity distribution in the first cross-sectional plane.
 2. The LEDlight unit according to claim 1, wherein the at least one chamfersurface extends around the entire perimeter of the refractive opticalelement.
 3. The LED light unit according to claim 1, wherein the chamferportion extends at most in the lower 50% of the refractive opticalelement, in particular at most in the lower 40% of the refractiveoptical element.
 4. The LED light unit according to claim 1, wherein therefractive optical element has at least one of the group of featurescomprising: the inner surface of the refractive optical element havingan inwards slanted chamfer surface refracting the light of the lightsource towards the support portion; the inner surface of the refractiveoptical element having an outwards slanted chamfer surface refractingthe light of the light source away from the support portion; the outersurface of the refractive optical element having an inwards slantedchamfer surface refracting the light of the light source towards thesupport portion; and the outer surface of the refractive optical elementhaving an outwards slanted chamfer surface refracting the light of thelight source away from the support portion.
 5. The LED light unitaccording to claim 4, wherein the inwards slanted chamfer surface of theinner surface of the refractive optical element has such an inclinationthat it refracts the light from the light source to a border surfacebetween the refractive optical element and the support portion.
 6. TheLED light unit according to claim 1, wherein the support portion islight-absorbent, at least in a border surface between the refractiveoptical element and the support portion.
 7. The LED light unit accordingto claim 1, wherein the support portion is reflective, at least in aborder surface between the refractive optical element and the supportportion.
 8. The LED light unit according to claim 1, wherein the lightsource has a source-side light intensity distribution, emitted from thelight source in operation, wherein the LED light unit has a desiredlight intensity distribution, emitted from the LED light unit inoperation, and wherein the at least one chamfer surface is designed insuch a way that a relative light intensity of the desired lightintensity distribution in the ambient light emission direction isreduced as compared to a relative light intensity of the sourcesidelight intensity distribution in the ambient light emission direction. 9.The LED light unit according to claim 8, wherein the at least onechamfer surface is designed in such a way that substantially no light isemitted in the ambient light emission direction.
 10. The LED light unitaccording to claim 8, wherein the desired light intensity distributionis defined by at least two cross-sectional light intensitydistributions, the at least two cross-sectional light intensitydistributions comprising a first desired cross-sectional light intensitydistribution in a first cross-sectional plane and a second desiredcross-sectional light intensity distribution in a second cross-sectionalplane, and wherein the inner surface and the outer surface of therefractive optical element are shaped such that they jointly transformthe source-side light intensity distribution into the desired lightintensity distribution.
 11. The LED light unit according to claim 1,wherein the light source is one single LED.
 12. The LED light unitaccording to claim 1, wherein a space between the light source and therefractive optical element is free of shutters and reflectors.
 13. Anaircraft, having at least one LED light unit according to claim 1, theat least one LED light unit being an exterior light of the aircraft. 14.A method of replacing a used light unit in an aircraft with an LED lightunit according to claim 1, the method comprising the steps of:disconnecting the used light from a power source, and connecting the LEDlight unit according to claim 1 to the power source.